Heat-sealable, hydrophobic, antibacterial bilayer nanocellulose/chitosan film for food preservation

Under the dual challenges of plastic-driven environmental pollution and global food insecurity, there exists an urgent demand for sustainable packaging solutions capable of extending produce shelf life. Cellulose nanofibers (CNF) and chitosan (CS) are promising bio-based materials; however, their susceptibility to performance loss in high-humidity environments and their lack of intrinsic heat-sealing capability limit practical applications. Herein, an asymmetric bilayer CNF/CS film crosslinked with genipin is introduced to effectively address the performance degradation under humid conditions. The film is hydrophobically modified with octanoic acid (OA), achieving an optimal balance of high transparency (visible-light transmittance >80%) and hydrophobicity (contact angle ≈ 110°). The inner layer, comprising thermoplastic starch (TPS) plasticized with polyvinyl alcohol (PVA) and blended with a thymol/octanoic acid deep eutectic solvent (DES), affords low-temperature processability and heat-seal performance (seal strength = 19.9 N / 15 mm) alongside potent antibacterial and antioxidant activity (inhibition > 98% against E. coli and S. aureus ). In strawberry and blueberry preservation trials, the resulting film completely suppresses mold growth within 5 days, with only 8% weight loss, and exhibits over 85% biodegradation in soil within 30 days. This bilayer design provides a new solution for developing high-performance, eco-friendly food packaging materials.